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천길정,한동철,Cheon, Gill-Jeong,Han, Dong-Chul 대한기계학회 1999 大韓機械學會論文集A Vol.23 No.7
Applying the conjugate contact condition, contact lines of a cylindrical worm gear has been calculated. The characteristics of tooth contact were analyzed and the pitting resistance were also assessed. It has been verified that: i) the length of contact is shortest on the 1st tooth of the front region, ii) the contact region is more narrow in the recess side than in the access side, iii) the contact region is more narrow in worm than in worm wheel. Hence, the pitting resistance is weakest in the recess side of the 1st contacting worm tooth.
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천길정 대한기계학회 1992 대한기계학회논문집 Vol.16 No.11
본 연구에서는 밸브판의 거동을 2차의 회전계로 간주하고, 양력 및 항력(drag force)을 구하는데 있어 Reif등이 구한것과 동일한 방법을 이용하되 정지핀에 의해 그 최대 열림각이 제한을 받는 물리적 사실을 고려하고, 밸브를 통과하는 유량도 단위 입 력이 아닌 정현파(sine wave)로 간주하여 밸브판의 동적거동을 해석하였다. 해석대 상의 밸브 모델로는 Bjork-Shiley 27mm 1엽 밸브를 선정하였다. In this paper, fluttering behavior of mechanical monloleaflet heart valve prosthesis was analyzed taking into consideration of the impact between the valve occluder and the stopper. The motion of valve occluder was modeled as a rotating system, and equations were derived by employing the moment equilibrium conditions. Lift force, drag force, gravity and buoyancy were considered as external forces acting on the valve occluder. The 4th order Runge-Kutta method was used to solve the equations. The results demonstrated that the occluder reaches steady eguilibrium position only after damped vibration. The mean damping ratio is in the range of 0.197-0.301. Fluttering frequency does not have any specific value, but varies as a function of time. It is in the range of 11-84Hz. Valve opening appears to be affected by the orientation of the valve relative to gravitational forces.
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스퀴즈필름효과를 고려한 인공심장밸브의 닫힘시 동적거동 해석
천길정 대한기계학회 1995 대한기계학회논문집 Vol.19 No.2
An analysis of the dynamics of a mechanical monoleaflet heart valve prosthesis in the closing phase is presented. Employing the moment equilibrium principles on the occluder motion and the squeeze film dynamics of the fluid between the occluder and the guiding strut at the instant of impact, the velocity of the occluder tip and the impact force were computed. The dynamics of fluid being squeezed between the occluder and the guiding struts is accounted for by Reynold's equation. The effect of the fluid being squeezed between the occluder and the guiding strut was to reduce the velocity of the occluder tip at the instant of valve closure as well as dampen the fluttering of the occluder before coming to rest in the fully closed position. The squeeze film fluid pressure changed rapidly from a high positive value to a relatively large negative value in less than 1 msec. The results of this study may be extended for the analysis of cavitation inception, mechanical stresses on the formed elements and valve components as well as to estimate the endurance limits of the prosthetic valves.
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세탁기용 트랜스미션을 모델로 한 기계 시스템 설계이론에 관한 연구
천길정,김완두,한동철,Cheon, Gil-Jeong,Kim, Wan-Du,Han, Dong-Cheol 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.2
본 연구에서 탐구된 새로운 설계조건과 설계원칙들을 적용함으로써 세탁기용 트랜스미션으로 대표되는 기계 시스템을 효과적으로 설계할 수 있었다. 개발된 자동설계 프로그램을 이용함으로써 다양한 설계시뮬레이션을 단기간에 수행할 수 있었으며 설계 실무자로 하여금 설계변수와 상태변수 등에 관한 민감도를 파악하게 하는데 매우 효과적이었다. 본 연구에서 새롭게 제안된 시스템 설계조건들과 설계원치기들은 세탁기용 트랜스미션 뿐만 아닌 일반적인 기계시스템 설계시에도 적용될 수 있는 것으로 판단된다. New design principles nad necessary conditions for a mechanical system have been suggested to be kept in the design process using a washing machine transmission as a model. The necessary conditions are funcitnal requirement condition and spatial arrangement condition. The design principles to satisfy the necessary conditions are the principle of sequence and the principle of expansion. Decision sequence for state variables and design varibles of various mechanicla elements have been formulated. New automatic design program for washing machine transmission has been developed observing the necessary conditions and design principles investigated in this study. It was verified to be very effective to follow the design conditions, principles nad formulated decision sequence in mechanical system design process.
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천길정 대한의용생체공학회 1991 의공학회지 Vol.12 No.3
In this paper, fluttering behavior of mechanical bileaflet heart valve prosthesis was analyzed taking into consideration of the impact between valve plate and stopper Vibration system of the valve was modeled as a rotating system, and equations are induced by moment equilibrium equations. Lift force, drag force, gravity and buoyancy were considered as external forces acting on the valve plate/ The 4th order Runge-Kutta method was used to solve the equations. Valve plate does not come to the static equilibrium position at a stretch, but come to that position after under damping vibration. Damping ratio increases as the cardiac optput increases, and the mean damping ratio is in the range of 0.16~40.25. Fluttering frequency does not have any specific value, but varies as a function of time. It is in the range of 10~40Hz. Valve opening appears to be affected by the orientation of the of the valve relative to gravitational forces.
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천길정 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.8
This paper describes an analysis of the nonlinear behavior of gear pairs according to the direct contact elastic deformation model over a wide range of speeds, considering the hydrodynamic effects and friction force. The inclusion of the hydrodynamic effect facilitates nonlinearity by increasing the overlap range (i.e., multiple solution regimes) and damping, as well as decreasing elastic deformation and tooth reaction forces. The effects of various lubrication parameters, such as viscosity and film width, on the nonlinear dynamic behavior were analyzed. While the viscosity has a strong effect on the behavior of gear pair systems, friction has very little effect on torsional behavior. Although the model of direct contact without friction has overall nonlinear behavior similar to the model including hydrodynamic effects with friction, the time data of these models are different due to the squeeze effect.
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천길정,이정한,한동철,Cheon, G.J,Lee, J.H,Han, D.C 대한기계학회 1997 大韓機械學會論文集A Vol.21 No.5
Decision process for length dimension in the mechanical system design process has been studied with a washing machine transmission as a model. The results are, (i) the length dimensions of the non-shaft elements are independent of other elements, (ii) the length dimensions of the shaft elements are dependent on the dimensions of the non-shaft elements located inside and outside of that elements, (iii) the length dimensions of the inner shaft elements are dependent on those of the outer shaft elements located parallel, (iv) the length dimensions of the shaft elements located serial are independent of each other.
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